Paul L. Durham

Regulation of calcitonin gene-related peptide secretion from trigeminal nerve cells by botulinum toxin type A: implications for migraine therapy.

Objective.—To determine the effect of botulinum toxin type A on calcitonin gene‐related peptide secretion from cultured trigeminal ganglia neurons.

Neuron-glia signaling in trigeminal ganglion: implications for migraine pathology.

Objective.—The goal of this study was to investigate neuronal–glial cell signaling in trigeminal ganglia under basal and inflammatory conditions using an in vivo model of trigeminal nerve activation.

Calcitonin Gene‐Related Peptide (CGRP) and Migraine

The neuropeptide calcitonin gene‐related peptide (CGRP) has long been postulated to play an integral role in the pathophysiology of migraine. While clinical findings are consistent with such a role, the specific pathogenic mechanisms of CGRP in migraine have remained speculative until recently. Through advances in molecular neuroscience, the pathogenic mechanisms of CGRP in migraine have begun to be elucidated. This paper discusses the hypothesized role of CGRP in migraine and reviews recent findings on the molecular mechanisms of this neuropeptide in migraine pathophysiology. Studies in cultured trigeminal neurons demonstrate that CGRP is released from trigeminal ganglia cells, that CGRP transcription is increased under conditions mimicking neurogenic inflammation, that migraine pharmacotherapies can both reduce CGRP release and inhibit CGRP transcription, and that tumor necrosis factor‐α (TNF‐α), an endogenous inflammatory mediator implicated in migraine, can stimulate CGRP transcription. Together, the results suggest that, in migraine, activation of trigeminal nerves release CGRP and other peptides that cause the release of proinflammatory mediators. These mediators further increase CGRP synthesis and release over hours to days in correspondence with the 4‐ to 72‐hour duration of a typical migraine episode. The increased CGRP synthesis and release might be mediated by activation of mitogen‐activated protein kinase pathways, which, in turn, can be modulated by endogenous inflammatory substances such as TNF‐α and affected by drugs such as sumatriptan.

Calcitonin gene-related peptide stimulation of nitric oxide synthesis and release from trigeminal ganglion glial cells

Clinical and basic science data support an integral role of calcitonin gene-related peptide (CGRP) in migraine pathology. Following trigeminal nerve activation, afferent release of CGRP causes vasodilation while efferent release leads to pain. Although CGRP can also be secreted from cell bodies of trigeminal neurons located within the ganglion, the function of CGRP released in the ganglion is poorly understood. Initially, we showed that SNAP-25, a protein required for CGRP release, was localized in cell bodies of trigeminal ganglia neurons. We also found that satellite glial cells in the ganglia express the CGRP1 receptor protein RAMP1. To determine whether CGRP could directly activate glial cells, primary cultures of rat trigeminal ganglia were utilized to study the effects of CGRP on glial nitric oxide (NO) synthesis and release. Under our culture conditions, >95% of the cells expressed glial fibrillary acidic protein and RAMP1. While weak iNOS staining was observed in glia under basal conditions, CGRP treatment greatly increased glial iNOS expression and NO release. This stimulatory effect was blocked by the CGRP1 receptor antagonist, CGRP(8-37) peptide. Treatment of glial cultures with forskolin or cAMP also increased iNOS expression and stimulated NO release to levels similar to CGRP. To our knowledge, this is the first evidence that activation of CGRP1 receptors regulates glial iNOS and NO release. We propose that following trigeminal nerve activation, CGRP secretion from neuronal cell bodies activates satellite glial cells that release NO and initiate inflammatory events in the ganglia that contribute to peripheral sensitization in migraine.

The effect of viscosity changes in the vocal folds on the range of oscillation

Summary Changes in vocal fold oscillation threshold pressure were induced in excised canine larynges by experimentally causing fluid movement into and out of the vocal folds. The transport was facilitated by exposing the vocal folds to various osmotic solutions, and it was assumed that changes in hydration caused changes in the internal tissue viscosity. A range of oscillation threshold pressures was measured for each condition of hydration by varying length and glottal width. The oscillation threshold pressure shifted as predicted. Decreased hydration (increased viscosity) raised the threshold of oscillation, and increased hydration (decreased viscosity) lowered the threshold of oscillation. This apparently represents the first in vitro model for the study of the effect of viscosity changes of the internal environment of the vocal folds on phonation.

Salivary Levels of CGRP and VIP in Rhinosinusitis and Migraine Patients

Background.—Secretion of calcitonin gene‐related peptide (CGRP) from trigeminal nerves and vasoactive intestinal peptide (VIP) from parasympathetic nerves is involved in the pathophysiology of migraine and rhinosinusitis. Analysis of these neuropeptides in human saliva samples can be used as markers of trigeminal and parasympathetic nerve activity in patients between and during attacks as well as in response to specific treatments.

Nitric oxide regulation of calcitonin gene-related peptide gene expression in rat trigeminal ganglia neurons

Calcitonin gene‐related peptide (CGRP) and nitric oxide are involved in the underlying pathophysiology of migraine and other diseases involving neurogenic inflammation. We have tested the hypothesis that nitric oxide might trigger signaling mechanisms within the trigeminal ganglia neurons that would coordinately stimulate CGRP synthesis and release. Treatment of primary trigeminal ganglia cultures with nitric oxide donors caused a greater than four‐fold increase in CGRP release compared with unstimulated cultures. Similarly, CGRP promoter activity was also stimulated by nitric oxide donors and overexpression of inducible nitric oxide synthase (iNOS). Cotreatment with the antimigraine drug sumatriptan greatly repressed nitric oxide stimulation of CGRP promoter activity and secretion. Somewhat surprisingly, the mechanisms of nitric oxide stimulation of CGRP secretion did not require cGMP or PI3‐kinase signaling pathways, but rather, nitric oxide action required extracellular calcium and likely involves T‐type calcium channels. Furthermore, nitric oxide was shown to increase expression of the active forms of the mitogen‐activated protein kinases Jun amino‐terminal kinase and p38 but not extracellular signal‐related kinase in trigeminal neurons. In summary, our results provide new insight into the cellular mechanisms by which nitric oxide induces CGRP synthesis and secretion from trigeminal neurons.

Tumor necrosis factor-α stimulation of calcitonin gene-related peptide expression and secretion from rat trigeminal ganglion neurons

Expression of the neuropeptide calcitonin gene‐related peptide (CGRP) in trigeminal ganglion is implicated in neurovascular headaches and temporomandibular joint disorders. Elevation of cytokines contributes to the pathology of these diseases. However, a connection between cytokines and CGRP gene expression in trigeminal ganglion nerves has not been established. We have focused on the effects of the cytokine tumor necrosis factor‐α (TNF‐α). TNFR1 receptors were found on the majority of CGRP‐containing rat trigeminal ganglion neurons. Treatment of cultures with TNF‐α stimulated CGRP secretion. In addition, the intracellular signaling intermediate from the TNFR1 receptor, ceramide, caused a similar increase in CGRP release. TNF‐α caused a coordinate increase in CGRP promoter activity. TNF‐α treatment activated the transcription factor NF‐κB, as well as the Jun N‐terminal kinase (JNK) and p38 mitogen‐activated protein (MAP) kinase pathways. The importance of TNF‐α induction of MAP kinase pathways was demonstrated by inhibiting MAP kinases with pharmacological reagents and gene transfer with an adenoviral vector encoding MAP kinase phosphatase‐1 (MKP‐1). We propose that selective and regulated inhibition of MAP kinases in trigeminal neurons may be therapeutically beneficial for inflammatory disorders involving elevated CGRP levels.

Calcitonin gene-related peptide promotes cellular changes in trigeminal neurons and glia implicated in peripheral and central sensitization

BackgroundCalcitonin gene-related peptide (CGRP), a neuropeptide released from trigeminal nerves, is implicated in the underlying pathology of temporomandibular joint disorder (TMD). Elevated levels of CGRP in the joint capsule correlate with inflammation and pain. CGRP mediates neurogenic inflammation in peripheral tissues by increasing blood flow, recruiting immune cells, and activating sensory neurons. The goal of this study was to investigate the capability of CGRP to promote peripheral and central sensitization in a model of TMD.ResultsTemporal changes in protein expression in trigeminal ganglia and spinal trigeminal nucleus were determined by immunohistochemistry following injection of CGRP in the temporomandibular joint (TMJ) capsule of male Sprague-Dawley rats. CGRP stimulated expression of the active forms of the MAP kinases p38 and ERK, and PKA in trigeminal ganglia at 2 and 24 hours. CGRP also caused a sustained increase in the expression of c-Fos neurons in the spinal trigeminal nucleus. In contrast, levels of P2X3 in spinal neurons were only significantly elevated at 2 hours in response to CGRP. In addition, CGRP stimulated expression of GFAP in astrocytes and OX-42 in microglia at 2 and 24 hours post injection.ConclusionsOur results demonstrate that an elevated level of CGRP in the joint, which is associated with TMD, stimulate neuronal and glial expression of proteins implicated in the development of peripheral and central sensitization. Based on our findings, we propose that inhibition of CGRP-mediated activation of trigeminal neurons and glial cells with selective non-peptide CGRP receptor antagonists would be beneficial in the treatment of TMD.

Sinus headache: a neurology, otolaryngology, allergy, and primary care consensus on diagnosis and treatment.

Sinus headache is a widely accepted clinical diagnosis, although many medical specialists consider it an uncommon cause of recurrent headaches. The inappropriate diagnosis of sinus headache can lead to unnecessary diagnostic studies, surgical interventions, and medical treatments. Both the International Headache Society and the American Academy of Otolaryngology-Head and Neck Surgery have attempted to define conditions that lead to headaches of rhinogenic origin but have done so from different perspectives and in isolation of each other. An interdisciplinary ad hoc committee convened to discuss the role of sinus disease as a cause of headache and to review recent epidemiological studies that suggest sinus headache (headache of rhinogenic origin) and migraine are frequently confused with one another. This committee reviewed available scientific evidence from multiple disciplines and concluded that considerable research and clinical study are required to further understand and delineate the role of nasal pathology and autonomic activation in migraine and headaches of rhinogenic origin. However, this group agreed that greater diagnostic and therapeutic attention needs to be given to patients with sinus headaches.